218 ACTUAL DURATION OP EFFECTS, 



quantities have been used ; there is much more of early than con- 

 tinued effect. Still, so far as known and "believed, there is always- 

 more or less of abiding effect, and which I infer will be permanent. 



But wider scope for observation has been afforded in the increas- 

 ing productiveness of all the marled lands, kept under what wa 

 deemed not too frequent tillage. Neither has the tillage been al- 

 ways mild, nor the rotation uniform ; and latterly the grain crops 

 have been made more frequent than before, and much more grazing 

 permitted.* Still, even where no prepared putrescent manures 

 have ever been applied, and putrescent matters have been furnished 

 only from the growth of the land itself during its share of rest in 

 each course of crops, there has been a regular increase of produc- 

 tiveness of the grain crops, in every successive rotation. [1842. J 

 In one connected clearing, of what I found as poor forest land, 

 now making 85 acres, the marling was commenced in 1818, and has 

 been continued, as the successive clearings extended, to 1841, 

 The earliest effects of the applications were always satisfactory, 

 but they have regularly and largely increased with time. Thus, 

 when under the last crop of corn (in 1839), the crop on the last 

 finished marling, though perhaps thereby nearly doubled in pro- 

 duct, was obviously and considerably less than that of four to sis 

 years earlier that again as inferior to that of the marling of ten 

 to fifteen years and the crop on the marling of 1821 and earlier, 

 decidedly the best of all, under circumstances otherwise equal. For 

 the limited time of twenty-three years, and without any careful and 

 accurate experiment or observation having been made for this special 

 object, there could not well be stronger practical proof of the per- 

 manency of the vegetable manures stored up by the marl. 



If we keep in mind the mode by which calcareous manure acts, 

 its effects may be anticipated for a much longer time than my ex- 

 perience extends. Let us trace the supposed effects, from the 

 causes, on an acid soil kept under meliorating culture. As soon 

 as applied, the calcareous earth combines with all the acid then 

 present, and to that extent is changed to the hum ate and other 

 vegetable salts of lime. The remaining calcareous earth continues 

 to take up the after formations of acid, and (together with the 

 salts so produced) to fix putrescent manures, as fast as these sub- 

 stances are presented, until all the lime has been combined with 

 acid, and all their product is combined with putrescent matter. 

 Both those actions then cease. During all the time necessary for 

 those changes, the soil has been regularly increasing in productive- 

 ness ; and it may be supposed that, before their completion, the 



* The land, however much improved in richness by being secured from 

 grazing so long, had in consequence become too "puffy" for wheat, and 

 also full of insects and bad weeds ; for all which grazing at some proper 

 timo of the rotation ia beneficial, and indeed essential. 



